U.S. patent number 4,700,543 [Application Number 06/813,724] was granted by the patent office on 1987-10-20 for cascaded power plant using low and medium temperature source fluid.
This patent grant is currently assigned to Ormat Turbines (1965) Ltd.. Invention is credited to Zvi Krieger, Alex Moritz.
United States Patent |
4,700,543 |
Krieger , et al. |
* October 20, 1987 |
**Please see images for:
( Certificate of Correction ) ** |
Cascaded power plant using low and medium temperature source
fluid
Abstract
A plurality of independent, closed Rankine cycle power plants,
each of which has a vaporizer, is operated by serially applying a
medium or low temperature source fluid to the vaporizers of the
power plants for producing heat depleted source fluid. A preheater
is provided for each vaporizer; and said heat depleted source fluid
is applied to all of the preheaters in parallel. The heat depleted
source fluid thus serves to heat the operating fluid to the
evaporization temperature, while the source fluid applied to the
vaporizers supplies the latent heat of vaporization to the
operating fluid of the power plant. The present invention is
advantageous, as compared to a conventional cascaded power plant of
the type described, because the temperature drop of the source
fluid can be increased without reducing the efficiency.
Alternatively, the temperature drop can be maintained but the
efficiency can be increased. In either case, the power produced by
the power plant according to the present invention is
increased.
Inventors: |
Krieger; Zvi (Tel Aviv,
IL), Moritz; Alex (Holon, IL) |
Assignee: |
Ormat Turbines (1965) Ltd.
(Yavne, IL)
|
[*] Notice: |
The portion of the term of this patent
subsequent to April 1, 2003 has been disclaimed. |
Family
ID: |
27091297 |
Appl.
No.: |
06/813,724 |
Filed: |
December 27, 1985 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
631058 |
Jul 16, 1984 |
4578953 |
|
|
|
Current U.S.
Class: |
60/655;
60/698 |
Current CPC
Class: |
F03G
7/04 (20130101); F01K 3/185 (20130101); F01K
23/02 (20130101) |
Current International
Class: |
F01K
23/02 (20060101); F01K 3/18 (20060101); F01K
3/00 (20060101); F03G 7/00 (20060101); F03G
7/04 (20060101); F01K 023/02 () |
Field of
Search: |
;60/655,698 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ostrager; Allen M.
Attorney, Agent or Firm: Sandler & Greenblum
Parent Case Text
This application is a continuation-in-part of copending application
Ser. No. 631,058 filed July 16, 1984 now U.S. Pat. No. 4,578,953.
Claims
We claim:
1. A power plant operating on a source of low or medium temperature
fluid comprising:
(a) a plurality of closed Rankine cycle power plant modules each
having a vaporizer associated therewith responsive to source fluid
for converting operating fluid of the power plant modules to vapor,
said modules being arranged in a plurality of levels, each level
comprising a plurality of modules;
(b) means for applying source fluid in parallel to each vaporizer
in a level to produce heat depleted source fluid, means for
applying heat depleted source fluid from a level to each vaporizer
in parallel in the succeeding level;
(c) a preheater associated with each vaporizer for preheating
operating fluid that is vaporized in the associated vaporizer;
and
(d) means for applying heat depleted source fluid from the lowest
level to all of the preheaters in parallel.
2. Apparatus according to claim 1 constructed and arranged so that
the modules are arranged into a plurality of levels, including
means for applying the heat depleted source fluid to all of the
preheaters in parallel independently of the levels of the
preheaters.
3. Apparatus according to claim 1 including means for applying the
heat depleted source fluid to all of the preheaters in parallel
independently of the levels of the preheaters.
4. A power plant according to claim 1 wherein said source is an
industrial fluid.
5. A power plant according to claim 1 wherein said source is
industrial waste heat fluid.
6. A method for operating a plurality of independent, closed cycle
power plant modules, each having a vaporizer and a preheater, said
method comprising the steps of:
(a) arranging the modules into a plurality of levels, each level
comprising a plurality of modules;
(b) applying a medium or low temperature source fluid in parallel
to each vaporizer in a level to produce heat depleted source
fluid;
(c) applying heat depleted source fluid from an upper level to each
vaporizer in parallel in the succeeding lower level; and
(d) applying heat depleted fluid from the lowest level to all of
the preheaters in parallel.
7. A method according to claim 6 including the step of arranging
the modules into a plurality of levels, and applying the heat
depleted source fluid to all of the preheaters in parallel
independently of the levels of the preheaters.
8. A method according to claim 6 including the step of applying the
heat depleted source fluid to all of the preheaters in parallel
independently of the levels of the preheaters.
9. A method according to claim 6 wherein the source fluid is an
industrial fluid.
10. A method according to claim 6 wherein the source fluid is
industrial waste heat.
Description
FIELD OF THE INVENTION
This invention relates to an improved cascaded power plant using
low and medium temperature source fluid.
DESCRIPTION OF PRIOR ART
Low and medium temperature source fluids, hereinafter termed source
fluids of the type described, are those fluids with a temperature
less than about 350.degree. F., such as geothermal fluids obtained
from many production wells, and industrial liquids produced by
various industrial processes. The East Mesa Development Project
located in the Imperial Valley of Southern California near
Holtville presently has six wells capable of producing about 4
million pounds per hour of geothermal fluid at about 324.degree. F.
Such geothermal fluid is an example of source fluid of the type
described.
Conventionally, electricity is produced from source fluids of the
type described using a closed Rankine cycle heat engine whose
operating fluid is an organic fluid (e.g., Freon), such system
being termed a power plant of the type described. A source fluid of
the type described is applied to a vaporizer of a power plant of
the type described containing liquid organic fluid whereby the
latter is converted into a vapor. The vapor is expanded in a
turbogenerator that converts some of the heat in the vapor to work
and produces heat depleted organic vapor that is condensed in a
condenser. The condensed organic fluid is returned to the
vaporizer, and the cycle repeats.
The condenser rejects the remaining heat in the heat depleted vapor
into ambient air, if an air cooled condenser is involved, or into
cooling water, if a water cooled condenser is used. Typically, the
vaporizer is operated at a pressure that produces saturated or only
slightly superheated vapor because the pressures involved are
relatively low and the design of the heat exchanger that
constitutes the vaporizer, the piping for conveying the vapor, and
the turbine, are simplified. In order to maximize power output of a
power plant of the type described, the temperature drop of the
source fluid across the entire heat exchanger system of the power
plant, and the evaporization temperature in the vaporizer must be
optimized.
The conventional cascaded power plant utilizes a plurality of
closed Rankine cycle power plant modules each having an associated
heat exchanger, the source fluid being serially applied to the heat
exchangers of each module. Whatever system is used, maximizing the
net power produced by the system is of paramount importance. One
technique for increasing the power is to extract more heat from the
source fluid by increasing its temperature drop. With either a
single stage or cascaded system, however, increasing the amount of
heat extracted from the source fluid by increasing the temperature
drop of the source fluid across the heat exchanger system has the
effect of decreasing efficiency of the power plant because the mean
temperature of the source fluid is reduced. This results in a
reduction of the evaporization temperature of the operating fluid
in the heat exchanger, thus reducing the Carnot efficiency of the
power plant.
In an effort to increase the efficiency of a power plant of the
type described, and to extract more power from the source fluid, it
has been proposed to operate at super critical temperatures and
pressures. In such case, the temperature of the vaporized organic
fluid produced by the heat exchanger system is higher than in the
above-described typical Rankine cycle power plant. While this
approach is effective to increase the efficiency of the power plant
and to increase its work output, the gains are offset by the higher
cycle pump power consumption, as well as increased cost and
complexity of the power plant whose pressure vessels must be
designed to operate at pressures in the range of 500-600 psia.
It is therefore an object of the present invention to provide a new
and improved power plant of the type described which can be
operated more efficiently than a conventional low pressure power
plant.
BRIEF DESCRIPTION OF INVENTION
The present invention provides a method for operating a plurality
of independent, closed Rankine cycle power plant modules, each of
which has a vaporizer, the method comprising the steps of serially
applying a medium or low temperature source fluid to the vaporizers
of the power plants for producing heat depleted source fluid,
providing a preheater for each vaporizer, and applying said heat
depleted source fluid to all of the preheaters in parallel. The
heat depleted source fluid thus serves to heat the operating fluid
to the evaporization temperature, while the source fluid applied to
the vaporizers supplies the latent heat of vaporization to the
operating fluid of the power plant.
The present invention is advantageous, as compared to a
conventional cascaded power plant of the type described, because
the temperature drop of the source fluid can be increased without
reducing the efficiency. Alternatively, the temperature drop can be
maintained but the efficiency can be increased. In either case, the
power produced by the power plant according to the present
invention is increased.
BRIEF DESCRIPTION OF DRAWINGS
An embodiment of the present invention is shown in the accompanying
drawings wherein:
FIG. 1 is a plot of temperature versus heat input for a heat
exchanger in a power plant of the type described showing the
relationship between the temperature drop of the source fluid and
the evaporization temperature of the operating fluid;
FIG. 2 is a block diagram of a cascaded power plant according to
the present invention;
FIG. 3 is a plot similar to FIG. 1 showing the temperatures at
various locations in the block diagram of FIG. 2; and
FIG. 4 is a plot like that of FIG. 3 for a conventionally cascaded
power plant having the same heat exchanger area as the power plant
whose operation is shown in FIG. 3.
FIG. 5 is a second embodiment of a cascaded power plant according
to the present invention showing a plurality of modular energy
converters arranged in multiple levels.
DETAILED DESCRIPTION
The problem with the prior art, which is solved by the present
invention, is illustrated in FIG. 1 to which reference is now made.
The plot shows the variation in temperature of source fluid as a
function of the rate of heat applied to a heat exchanger in a
single-stage power plant of the type described. Curve A represents
the cooling of source fluid in a heat exchanger from temperature
T.sub.in, at the entrance to the heat exchanger, to temperature
T.sub.out1, at the outlet of the heat exchanger, where T.sub.in
-T.sub.out1 =Del T.sub.1. In a known way, the evaporization
temperature T.sub.evap1 of the operating fluid, whose variation is
indicated by curve B, is determined by the temperature of the
operating fluid entering the heat exchanger, T.sub.cond, and Del
T.sub.1. The ratio a.sub.1 /b.sub.1 is termed the percentage of
preheat for the heat exchanger, which is the ratio of the amount of
heat per unit time required to raise the operating fluid from the
condenser temperature to the vaporization point (remaining in
liquid form), to the total amount of heat per unit time required to
evaporate the operating fluid. For source fluids of the type
described, this ratio may range from 25% to 55%.
The difference between temperature T.sub.pp1 of the source fluid at
the break-point of curve B, and T.sub.evap is termed the
pinch-point temperature; and this temperature is conventionally in
the range 8.degree.-12.degree. F. It can be shown that reducing the
pinch-point temperature to increase the evaporation temperature has
the effect of increasing the efficiency of the system, because the
Carnot efficiency is proportional to the ratio of the difference
between the evaporation and the condenser temperatures to the
evaporization temperature in absolute units. However, it can be
shown that increasing the Carnot efficiency in this manner will
occur at the expense of the disproportionately large increase in
surface area of the heat exchanger.
To increase the power output of a power plant using an operating
fluid according to curve B and a source fluid cooled according to
curve A, increasing the temperature drop of the source fluid may be
appropriate. In such case, the source fluid is cooled according to
curve C from T.sub.in to T.sub.out2 ; and the operating fluid will
then be described by curve D. That is to say, T.sub.evap2 will be
lower than T.sub.evap1. Moreover, it can be shown that while the
heat extracted from the source fluid increases as the cooling of
the source fluid increases, the efficiency of the system will
decrease. Whether the power output increases will depend upon the
rate at which cooling of the source fluid occurs in the heat
exchanger. The problem of increasing the power output is addressed
and solved by the present invention.
Referring now to FIG. 2, reference numeral 10 designates a power
plant according to the present invention. Power plant 10 comprises
a plurality of independent closed, Rankine cycle organic fluid
power plant modules 12A, 12B and 12C. Three such power plant
modules are shown; but the invention is applicable to two or more
independent power plant modules. Each of these modules is identical
and as a consequence, only module 12A is described in detail. This
module includes vaporizer 13A containing an organic liquid, and to
which a low or medium temperature source fluid from source 11 is
applied via inlet 14A. The organic liquid contained within
vaporizer 13A is vaporized producing essentially saturated or
slightly superheated vapor which is applied to turbine 16A of
turbogenerator 15A. The vapor expands in turbine 16A, and some of
the heat contained in the vapor is converted into work as generator
17A produces electrical power. The vapor exhausted from turbine 16A
is applied to condenser 18A wherein the vapor is condensed into
liquid by the application to the condenser of cooling water.
Alternatively, an air cooled condenser can be used.
By means of a pump (not shown), condnsate from condenser 18A is
transferred into preheater 19A that may be a physical part of, or
separate from vaporizer 13A. Heat depleted source fluid, obtained
from the outlet from the vaporizer of the third module, is applied
to preheater 19A at inlet 20A to the preheater; and the cooled
source fluid is transferred at outlet 21A. If the source fluid is
geothermal, the cooled fluid may be transferred to a rejection
well; or, if the source fluid is an industrial chemical, the cooled
fluid may be transferred back to the process.
As shown in FIG. 2, source fluid that exits from vaporizer 13A at
outlet 22A is applied to the inlet 14B of vaporizer 13B of power
plant module 12B; and the source fluid that exits from vaporizer
13B at outlet 22B is applied to inlet 14C of vaporizer 13C of
module 12C. The source fluid that exits from vaporizer 13C at 22C
is, hereinafter, termed heat depleted source fluid because of the
heat extracted in each of vaporizers 13A, 13B and 13C. This heat
depleted fluid is applied to each of the preheaters 19A, 19B and
19C, in parallel. That is to say, the present invention provides
for serially applying a low or medium temperature source fluid from
source 11 to vaporizers 13A, 13B, and 13C of power plants 12A, 12B,
12C for producing heat depleted source fluid which appears at the
outlet 22C of vaporizer 13C; and, the heat depleted source fluid is
applied to each preheater 19A, 19B, and 19C in parallel. The source
fluid that exits from the preheaters is conveyed to a rejection
well if the source fluid is geothermal.
FIG. 3 shows a typical temperature-heat diagram for a power plant
like that shown in FIG. 2 capable of operating with geothermal
fluid produced by the East Mesa Field described above. The values
of temperature and flow rates are based on the current capability
of the East Mesa Field and are for the purpose of comparing the
power produced by a power plant according to the present invention
and a conventional cascaded power plant using heat exchangers with
the same total area.
Approximately 3.7 million pounds per hour of geothermal fluid is
available for serial input to vaporizers 13A, 13B and 13C; about
half of the heat depleted geothermal fluid that exits from
vaporizer 13C is applied to preheater 19A, about 1/3 is applied to
preheater 19B, and the balance to preheater 19C. It is assumed that
the condenser conditions ar such that the temperature of the
organic fluid that exits from the condenser of each module of the
power plant is 100.degree. F., that the temperature of the heat
depleted geothermal fluid exiting from vaporizer 13C is 175.degree.
F., and that the heat depleted geothermal fluid is further cooled
on passing through each preheater to 130.degree. F.
Geothermal fluid enters vaporizer 13A at 324.degree. F. and is
cooled by transit through the vaporizer to a temperature of
247.degree. F. The organic liquid contained within vaporizer 13A is
heated in temperature from 168.degree. F. to 268.degree. F. which
is the evaporation temperature for power plant module 12A. This
provides a pinch point temperature of about 8.degree. F. The
temperature of the geothermal fluid that exits from vaporizer 13C
is 175.degree. F. and the geothermal fluid is cooled from this
temperature to 130.degree. F. in each of preheaters 19A, 19B, and
19C. Thus, for power plant module 12A, the geothermal fluid is
cooled from 175.degree. F. to 130.degree. F. while the organic
liquid in the preheater is warmed from 100.degree. F. to
168.degree. F.
The evaporation temperature in power plant 12B is 203.degree. F.
which, of course, is less than the evaporation temperature in power
plant 12A. Thus, the operating pressure of power plant 12B is less
than the operating pressure in power plant 12A. Similarly, the
evaporation temperature in power plant 12C is 168.degree. F. which
is the lowest temperature of the three power plants.
It can be shown that the overall log-mean-temperature-difference
(LMTD) for the heat exchangers of modules 12A, 12B and 12C is about
23.degree. F., about 19.degree. F., and about 16.degree. F.,
respectively. Furthermore, it can be shown that the Carnot
efficiency for the power plant illustrated in FIG. 3 is about
18.5%. A conventional three-stage cascaded power plant having heat
exchangers of substantially the same area as the power plant of
FIG. 3 will have a temperature-heat diagram like that shown in FIG.
4. In such conventional power plant, the geothermal fluid is cooled
from 324.degree. F. to 130.degree. F. in one serial pass through
the heat exchangers. In the three modules, the evaporation
temperature will be 272.degree. F., 178.degree. F., AND 129.degree.
F., respectively. The geothermal fluid will have a temperature of
225.degree. F. entering the heat exchanger of the second module,
and a temperature of 168.degree. F. entering the third module. In
such case, it can be shown that the LMTD of each module of such a
cascaded system is about 23.degree. F., 19.degree. F., and
17.degree. F., respectively. This establishes that the surface area
of the heat exchangers in the conventional system is almost
identical to the surface area of the heat exchangers of the power
plant according to the present invention. However, the Carnot
efficiency of the conventionally cascaded power plant is only about
16.7%. Thus, a power plant according to the present invention, with
the same sized heat exchangers as in a conventional cascaded power
plant will produce over 10% more power without a significant
increase in cost.
A second embodiment of the invention is shown in FIG. 5 wherein a
plurality of modular energy converters like those shown in FIG. 2
are organized so as to permit a power plant of almost any capacity
to be constructed by selecting a suitable number of converters.
Power plant 100 shown in FIG. 5 thus comprises a plurality of
modules arranged in a plurality of levels. Three levels are shown
in the drawing, but both the number of levels, and the number of
modules in each level are selected in accordance with the required
capacity of the power plant. Thus, as an example only, the power
plant shown in FIG. 5 comprises nine modules arranged in three
levels of three modules each.
Each module 101A-C in level 1, each module 102A-C in level 2, and
each module 103A-C in level 3, comprises a vaporizer, a preheater,
an organic fluid turbogenerator (not shown), and a condenser (not
shown) organized in the manner shown in FIG. 2. Thus, in module
101A, for example, an organic fluid, such as Freon or the like, is
heated and transferred to vaporizer 105A where vaporization takes
place. The vaporized organic fluid is piped to the turbogenerator
where expansion takes place driving an electrical generator which
produces power, and heat depleted vapor that is condensed in the
condenser of the module and returned to the preheater.
According to the present invention, geothermal source fluid from a
well (not shown) is applied in parallel via header 106 to each
vaporizor in the level 1 modules, collected at the exit of these
modules, and then applied in parallel via header 107 to the
vaporizers in the level 2 modules, etc. The heat depleted
geothermal fluid is collected in header 108 at the outlet of the
level 3 vaporizers and applied, in parallel to all of the
preheaters. Thus, each column of the three vertically aligned
modules shown in FIG. 5 corresponds to the arrangement shown in
FIG. 2. A power plant organized like that shown in FIG. 5 is
particularly useful when the source of geothermal fluid produces
fluid in sufficient volume to supply multiple power plants arranged
like that shown in FIG. 2.
It is believed that the advantages and improved results furnished
by the method and apparatus of the present invention are apparent
from the foregoing description of the preferred embodiment of the
invention. Various changes and modifications may be made without
departing from the spirit and scope of the invention as described
in the claims that follow.
* * * * *